Method of differentially heat treating a cutter bar



April 22, 1953 A. E. BRIDGE ETAL 2,831,788

METHOD OF DIFFERENTIALLY HEAT TREATING A CUTTER BAR Original Filed Feb.23, 1950 2 Sheets-Sheet 1 M N 0 0 1 M65 EDB mmv ms T MW B D A A W B TmATTORNEYS April 22, 1953 A. E. BRIDGE ETAL 2,831,788

METHOD OF DIFFERENTIALLY HEAT TREATING A CUTTER BAR Original Filed Feb.25, 1950 2 Sheets-Sheet 2 Q em 3 R 3 @m e w 0 w M. mw w M/ W 05 M 1.] m.m R S w m m L 56 m Mm mm 5 A @mvw H mm kt mt v@ mm Om Om Q United StatesPatent METHOD OF DIFFERENTIALLY HEAT TREATING A CUTTER BAR Adam E.Bridge, Franklin, and Albert G. Gibson, Middletown, Ohio, assignors toThe Black-Clawson Company, Hamilton, Ohio, a corporation of OhioOriginal application February 23, 1950, Serial No. 145,838, now PatentNo. 2,686,460, dated August 17, 1954. Divided and this application April29, 1954, Serial No. 426,532

13 Claims. (Cl. 148-105) This invention relates to cutter bars or knivesfor refining apparatus of the type utilized for the treatment ofcellulose fibers and the like in the preparation of paper making stock.

The invention has particular application to cutter bars for refinerssuch as Jordans and beaters wherein a plurality of bars are carried by aplug or other rotating member in such manner that they are arrangedgenerally axially of the axis of the plug with their outer edges exposedfor working on the fibers in the stock, the invention being applicableto both the bars carried by the rotating member and also to thecooperating stationary bars such as in the shell of a Jordan. Theseouter edges of the bars accordingly constitute their working edges whichare subjected to a major portion of the wear in operation, and it isdesirable that they possess adequate hardness to Withstand continued useover long periods and that the degree of hardness along these workingedges be properly correlated with the degree of toughness required inthe remainder of the bar, including the portion secured to the plug orother rotating member.

For example, in a common construction of bars for the plug of a Jordan,the cutter bars are retained on the plug by means of a series of ringsinterfitting with hook portions of the bars which are formed along theirinner edges and are subjected to substantial stresses, includingcentrifugal force, during operation. These working stresses areaccordingly of importance in determining the degree of hardness whichcan be imparted to the bar as a whole without having the hook portionsbecome so brittle as to be in danger of breaking in use. If the bar isof optimum hardness for the working edge, it would be too brittle alongthe hook portions of the bar. On the other hand, if the bar is ofoptimum toughness for the hook portions, the working edge would not behard enough and would tend to erode too rapidly and to burr, formingsharp edges which would cause cutting of the fibers instead of thedesired rubbing action, and if it is attempted to overcome thesedisadvantages and to obtain different degrees of hardness and toughnessalong the edges of the bar by means of a surface or edge coating or bywelding or otherwise securing a harder working edge portion to a backingof tougher metal, the cost of production tends to become too high tocompensate for such improved results as may be obtained.

The usual result for bars which are uniformly heat treated in a furnaceis accordingly a compromise, with a resultant shorter useful life thanif the bar were differentially hardened to give the desired hardness ortoughness at each point. A further factor atfecting the useful life ofsuch uniformity heat treated bars is that with the hook portions formedtherein by punching before the heat treatment, scratch lines are formedtransversely of the bar which constitute stress points at which crackstend to develop during the subsequent heat treatment, thus materiallyweakening the bar and increasing the possibility of breakage of thesehook portions. Similar disadvantages exist in the case of such barswhich do not have hook or lug portions in that the back edge portion ofthe bar must be tough enough to prevent premature failure.

It is accordingly one of the principal objects of the present inventionto provide a cutter bar of the above character which is integrallyformed, as distinguished from a welded or other composite structure, andwhich possesses properties of differential hardness and toughness acrossthe width thereof such that a minor portion of the bar extendinglengthwise of and including its working edge is hardened to apredetermined high degree of hardness while the remainder of the barincluding its opposite edge portion is substantially less hard and formsa tough supporting portion for the hardened working edge.

Bars having these desired characteristics are produced in accordancewith the invention by a controlled method of heat treatment in which theheat is applied successively to different localized portions of the barto obtain the desired properties of differential hardness and toughness.Thus in the first heating step, the heat is applied only to the minorportion of the bar along its working edge where maximum hardness isdesired in the finished bar, this step being readily carried out bypassing the bar through a high frequency induction field of highintensity which is limited in its effective cross-sectional dimensionsto receive only the desired limited portion of the bar therethrough.This portion of the bar is thus heated very rapidly to a predeterminedhigh temperature, and it is then immediately quenched with a suitablefluid such as oil in order to limit the cross-sectional area of the barin which the hardening takes place.

Following quenching, heat is again applied to the bar but only to thedirection thereof along its back edge which was not directly heatedduring the first heating step, and this second heating step maysimilarly be carried out by means of a high frequency induction field,with the intensity of this field and hence the heating eifect beinglower than that of the first step to limit the temperature reached inthe bar during this second heating step to a lower range such that thetemper is drawn from the back edge portion of the bar. This secondheating step is readily carried out before the bar has cooled completelyfrom the first heating step, and in fact while another portion of thesame bar is undergoing the first heating step, and it has been founddesirable to cool the bar slowly in air at room temperature afterdrawing rather than to quench it. During this slow cooling, heat willflow by conduction to the working edge portion of the bar to asufficient extent to effect reduction in the hardness therein ascompared with the hardness imparted thereto during the first heatingstep, and thus in the finished bar the portion of the bar where weartakes place in use is hardened as desired, while the balance of the baris substantially less hard. It is also found that with the drawing heatthus applied to the back portion of the bar followed by slow cooling,such warping as may tend to take place along the bar as a result of thefirst heating step is substantially compensated for without requiringadditional corrective treatment.

This method not only is capable of continuously producing cutter barshaving the properties of diiferential hardness and toughness referredto, but it also offers the advantage of ready control of the degree ofhardness and toughness in the several portions of the bars by suitableadjustment of the draw temperature. This is particularly advantageous inview of the fact that different degrees of hardness are desired incutter bars for Jordans and other refiners depending upon the particularstock to be worked on and the particular type of paper for which thestock is intended. With the method of the present invention, adjustmentof the intensity of one or both O of the induction fields employed inthe heating steps, and of the temperature and pressure of the quenchingfluid, will control the hardness properties of the finished bars, andafter the proper set of conditions is determined, each of a plurality ofsuccessive bars treated under these conditions will be found to possessuniformly the desired properties of differential hardness and toughness.

It is accordingly another object of the invention to provide a simple,economical and practical method of heat treating cutter bars of theabove character under controlled conditions such that the degree ofhardness of the finished bar is readily predetermined and controlled anda desired high degree of hardness is obtained along the working edge ofthe bar while the portion of the bar along its back edge in which theretaining hook portions are formed is of a substantially lower degree ofhardness and substantially greater degree of toughness for withstandingthe centrifugal force and other stresses on the bar incident to usethereof.

It is also an object of the invention to provide simple apparatus forcontinually heat treating successive cutter bars of the above characterby induction heating under controlled conditions such that the workingedge portion of each bar is hardened to a predetermined extent While theopposite edge portion of the bar is caused to become substantially lesshard and substantially tougher than the working edge, and whereinprovision is made for ready adjustment and control of the heatingconditions in accordance with the particular degree of hardness ortoughness desired in different portions of each bar.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

In the drawings- Fig. l is a view in side elevation of a Jordan barconstructed in accordance with the invention;

Fig. 2 is a diagrammatic perspective view illustrating successive stepsof the heat treating method for producing the bar of Fig. 1;

Fig. 3 is a side elevation of the Jordan plug;

Fig. 4 is an enlarged detail view in section showing one of the barsmounted in the Jordan plug;

Fig. 5 is a fragmentary side elevation of the mounting or back edgeportion of the bar of Fig. 4 and including one of the hook portionstherein;

Fig. 6 is a graph aligned with Figs. 4 and 5 to show respectively thetypical hardness of the bar from edge to edge before heat treatment,after hardening but before drawing, and in the finished bar after bothhardening and drawing;

Fig. 7 is a diagrammatic plan view of apparatus in accordance with theinvention for carrying out the heat treating method;

Fig. 8 is a fragmentary side elevation of the apparatus of Fig. 7;

Fig. 9 is an enlarged detail view in section on the line 9-9 of Fig. 8;and

Fig. 10 is an enlarged detail view in section on the line 10-10 of Fig.8.

Referring to the drawings, which illustrate a preferred embodiment ofthe invention, Fig. 1 shows a Jordan bar on which the working edge isidentified as 20, and which has hook portions 22 formed along its edge23 opposite working edge for engaging the usual retaining rings of theJordan plug, the complete plug being shown at 25 in Fig. 3. A lug 26 isformed at one end of the bar to receive the usual keeper ring 27 at thesmaller end of the plug, and bar 15 also has a head 28 which runs alongeach side thereof approximately midway between the working edge 20 andback edge 23. The bar 15 as shown is one of many designs of cutter bars,both rotating and stationary, adaptable and responsive to differentialheat treatment in accordance with the invention to give it properties ofdifferential hardness and toughness such that a minor portion thereofrunning along the working edge .20 is hardened to a 4 comparatively highdegree in order to give the desired resistance to abrasion in thisportion of the bar, while the portion of the bar extending along itsback edge 23 and including the hooks 22 is substantially less hard andsubstantially tougher than the working edge to support the bar on theplug during operation of the Jordan.

A controlled method of heat treatment for imparting these properties tosuccessive cutter bars is illustrated diagrammatically in Fig. 2, whichshows a plurality of bars 30 arranged in end-to-end relation for travelin the direction indicated by the arrow 31 through a pair of highfrequency induction heating fixtures 33 and 34. As shown, the fixture 33includes a portion of generally saddle shape arranged to straddle thelimited portion of the bar which is intended to form the working edge inthe finished bar, shown as its upper edge, and fixture 33 isproportioned to receive only about one-quarter of the width of the bar.This fixture includes an induction coil which is supplied with currentat a predetermined high wattage to create the desired high intensityfield across the portion of the fixture through which the upper edge ofeach bar 30 passes.

The drawing fixture 34 is of channel shape and of such proportions as toreceive approximately the entire lower portion of each bar 30 which wasexcluded from the hardening coil fixture 33, i. e., the lowerapproximately three-quarters of the bar, and fixture 34 is shown asspaced from fixture 3-3 but suificiently close thereto to receive theleading end of each bar before its trailing end has left fixture 33.This fixture 34 also includes a high frequency induction coil, and incarrying out the above method, it is supplied with current at apredetermined wattage lower than the hardening coil of the fixture 33 toeffect heating of the portion of the bar passing therethrough to apredetermined lower temperature than is reached in the portion of thebar heated by the fix ture 33.

A fixture indicated generally at 35 is provided for applying quenchingfiuid to the edge portion of the bar heated in the fixture 33, thisquenching fixture 35 being preferably arranged as shown to discharge astream of oil against each side of the heated edge portion of the bar.It has been found desirable to apply the quenching oil at substantialpressure and constant temperature in order to produce rapid cooling ofthe heated working edge portion of the bar before the correspondingpoint on the opposite edge of the bar reaches the drawing fixture 34,and the quenching fixture 35 is accordingly positioned closely adjacentthe hardening fixture 33, this immediate and rapid quenching being alsodesirable in minimizing distortion of the bar as a result of the edgehardening step. The application of the drawing heat at the fixture 34only along the back edge portion of the bar is also of materialimportance in controlling and preventing distortion of the bar and thussubstantially eliminating the necessity for further correctivetreatment.

Further control over the temperatures reached in the bar and thusincreased accuracy of control over the hardness properties in thefinished bars is obtained by regulating the temperatures of the fixtures3-3 and 34 themselves, as by circulating a cooling fluid through thefixtures as indicated at 36 and 37. This may be readily andsatisfactorily done by connecting the two fixtures with the same sourceof quenching fluid used to supply the quenching fixture 35. Also, inorder to rcducc burr ing of the quenching oil as the bars pass throughthe drawing fixture 34, an air blast 38 may be locutol as shown betweenfixtures 34 and 35 to strip excess oil from each bar before it reachesfixture 34.

The power input to each of the coil fixtures 33 and 34. and hence thetemperature reached in the her during the heating and drawing steps, isreadily predetermined and controlled in accordance with the initialcomposition of the bar and the desired final properties of differentialhardness and toughness, and these properties are further afiected by therate of travel of the bars through the fixtures and also by thetemperature and pressure of the quenching fluid. For example, Figs. 4 to6 illustrate these properties of a section of a bar 15 treated asdescribed in connection wtih Fig. 2 and having substantially thefollowing initial percentage composition:

Carbon 0.60 to 0.70 Manganese 0.70 to 0.80 Phosphorus s 0.04 max.Sulphur 0.04 max. Silicon 0.20 to 0.30 Nickel 0.40 to 0.50 Chromium 0.30to 0.40 Molybdenum 0.20

Iron Balance Fig. 6 illustrates the changes in the hardness propertiesof a typical bar 15 of this composition resulting from treatment by themethod as illustrated in Fig. 2 under the following conditions:

Bar width inches 2% Bar thickness do A Rate of bar travel -inches perminute 24 Power input to hardening fixture "kw" 23 Distance betweenhardening and quenching fixtures inches 1 Distance between hardening anddrawing fixtures inches 12 Quenching fiuid temperature F 98 Quenchingfluid pressure pounds per sq. inch" 10 Power input to drawing fixture kw17 Under these conditions, with the dimensions of the hardening fixture33 such as to give an effective length of approximately 4 inches for thefield therein, the upper edge portion of the bar reaches a temperatureof the order of 1575 F. With the quenching fluid applied to the barsubstantially immediately at the temperature and pressure indicated, thetemperature of the upper portion of the bar will drop to a range of theorder of 400 to 500 F. before the bar reaches the drawing fixture 34,and with the dimensions of this fixture 34 such as to give an effectivelength of approximately 9 inches for the field therein, the drawingtemperature in the lower portion of the bar will reach approximately1200" F. Also, although the heat is applied in this fixture only to theprevious unheated portion of the bar, there will be a flow of heat byconduction to the upper edge 20 of the bar to raise its temperaturematerially, to a range of the order of 1000 F., and similarly during thesubsequent air cooling period, the temperature throughout the entire barwill be substantially equalized by conduction.

In Fig. 4, the bar 15 is shown fragmentarily as mounted in the Jordanplug 25 with its hard working edge 20 outermost, and the graphs in Fig.6 are aligned with Figs. 4 and to illustrate the changes in the hardnessof the bar from edge to edge resulting from heat treatment under theabove operating conditions. The continuous line 40 represents theinitial hardness of the bar before treatment as measured on the RockwellC scale, and it will be noted that this hardness is uniform across theentire width of the bar at a value of approximately 28 Rockwell C. Thelong and short dash curve 42 shows the hardness of the bar followinghardening in the fixture 33 and quenching but before drawing. As shown,the hardness of the bar along and adjacent its working edge 20 isincreased to between 60 and 62 Rockwell C, but the hardened area coversonly a little over a quarter of the width or the bar, with the hardnessdropping sharply to a range not materially different from that of theuntreated bar over the remaining portion of its width.

-The curve 44 comprising short dashes shows the hard ness of the barfollowing completion of the drawing step in the fixture 34 andsubsequent air cooling at room temperature. It will be noted that thehardness at the working edge 20 has been reduced to approximately 39Rockwell C, and this hardness is relatively uniform near the edge 20 andover approximately one-quarter of the width of the bar. at which pointit drops sharply to about 27 Rockwell C. The hardness remains in thisrange across the adjacent intermediate portion of the bar, which isapproximately equal in extent to the hard portion, and then it againdrops comparatively rapidly at about the middle of the bar to a rangebetween approximately 20 and 22 Rockwell C across the remainingapproximately 50% of the width of the bar.

In other words, following completion of the heat treatment under theabove conditions, the bar comprises a minor portion, amounting to aboutone-quarter of its width, extending along and including the working edgewhich has a hardness substantially greater than the initial hardness ofthe untreated bar. At the same time, approximately one-half the width ofthe bar, including its back edge 23 and the hook portion 22, has ahardness which not only is substantially lower than that along theworking edge but is materially lower than the initial hard ness of theuntreated bar. The intermediate portion of the bar which connects thehard and soft portions is of an intermediate range of hardness notmaterially different from that of the untreated bar.

These properties of differential hardness and toughness can be obtainedwith a high degree of uniformity in a plurality of successive bars ofthe same composition which are heat treated as described under the sameconditions. A full set of bars of substantially identical hardnessproperties for the plug or shell of a refiner or beater can thus beproduced by this method, as contrasted with sets of bars heat treated asa batch according to the usual practice, since when a set of bars isbatch treated in a furnace, it is commonly found that all bars in theset are not heated to the same extent and that the quenching conditionsare not uniform for all bars in the set. These non-uniform results areavoided in the method of the present invention, which provides fortreatment of each successive bar of a set under identical conditions.

Different degrees of hardness in the bars can also be obtained byadjustment of the operating conditions in accordance with the desiredresults in the finished bar. Thus in the above example, the hardness ofthe bar along its working edge can be changed as desired by appropriateadjustment of the power input to the drawing coil 34. For example, ifthe power input is reduced from 17 kw. to 15 kw., the hardness along theworking edge of the bar will measure in the neighborhood of 42 RockwellC, and if the power input is increased to 19 kw., the hardness of theworking edge 20 will be reduced to the neighborhood of 33 Rockwell C.Also, the rate of travel of the bars through the heating fixtures is ofimportance in determining the temperatures to which the several portionsof the bars are heated. For example, in order to obtain the sameproperties as shown in Fig. 6 in bars of or /3 inch in thickness, therate of travel should be reduced to from 20 to 22 feet per minute if theother operating conditions remain the same, and similarly for a bar of iinch thickness, the rate of travel should be increased to from 28 to 30feet per minute.

It will thus be apparent that the properties desired in each portion ofthe bar can be effectively determined in advance and produced insuccessive bars as desired. As a result, it is possible and practical inaccordance with the invention to obtain bars for the plug or shell of aJordan or other refiner which are harder along their working edges thanthe bars previously obtainable by methods of heat treatment in which thehardness along the working edge required compromise with the degree oftoughness necessary along the supporting edge of the bars. Also, sinceas noted the method of the operation makes possible the reduction of thedegree of hardness along the back edge of the bar as compared with theinitial hardness of the untreated bar, when mounting hooks or lugs suchas the hooks 22 are desired, they can be formed therein by punchingafter heat treatment, thus eliminating the development of cracks at thehook portions such as tend to be caused when the hooks are punched priorto heat treatment of the bars.

Figs. 7 to illustrate more or less diagrammatically a machine forcontinuously performing the heat treating method described in connectionwith Fig. 2. The main body of the machine is shown as an elongatedchannel arranged on one edge and having a plate 51 secured within itsopen side and a front cover 52, and the base of the machine is indicatedgenerally at 53. The induction coil fixture 33 is shown as supported ona housing 55 containing its associated electrical equipment. and thedrawing coil fixture 34 is similarly supported by a housing 56 for itsassociated electrical apparatus.

The quenching fixture 35 is shown as supported by a bracket 61 adjacentthe hardening coil, and this fixture is shown as a quench ring adaptedto receive the upper portion of the bar 30 as shown fragmentarily inFig. 10. The quenching oil is supplied to the ring 60 by a pair of pipes62 which are connected by a hose 63 and valve 64 with a main oil supplypipe 65 running along the front of the machine. This pipe is in turnsupplied with oil under pressure by means of the pump 66 and reservoir67, and the oil is maintained at constant temperature by circulationthrough a cooling chamber 68 supplied with a suitable cooling mediumsuch as water as indicated at 69.

The channel 50 supports a series of driven conveyor units 70 forcontinuously conveying the bars 30 through the coils 55 and S7 and thequenching ring 60. Referring to Fig. 9, each of these conveyor unitsincludes a quill 71 supported by the channel 50 and plate 51 and havinga spindle 72 rotatably mounted therein by means of bearings 73 and 74.At its inner end, each spindle carries a friction wheel 75 counterboredon one side to receive a smaller friction wheel 76 having a serrated orotherwise roughened periphery. A wheel 77 is positioned between thefriction wheel 76 and a shoulder 78 on the spindle, and a coil spring 80is held in engagement with the outer face of friction wheel 75 by a nut81 threaded on the end of the spindle. These parts are proportioned toform a groove between the wheels 75 and 77 for receiving the lower edgeportion of the bar 30. with the spring 80 serving to maintain axialpressure on the bar between wheels 75 and 77.

The outer or forward end of each spindle 72 carries a sprocket wheel 83,and a chain 84 engages each sprocket 83 and the two end sprockets 85 and86. The end sprocket 85 is shown as on the same shaft with a sprocket 87driven through chain 88 and sprocket 89 by a motor 90 provided with avariable transmission such as a Reeves drive 91 for adjusting the speedof sprocket 89. The end sprocket 86 has a tensioned mounting comprismg afork 92 extending through the end plate 93 and carrying a spring 94 heldunder compression against plate 93 by nut 95. A guard 96 extends alongthe channel 50 above the sprockets 83 to insure proper drivingcngagement of the chain 84 with each sprocket.

With this arrangement, the spindles 71 are all positively driven andthus cause rotation of the wheels 75. 76 and 77 to convey the successivebars 30 lengthwise of the machine and through the hardening and drawingcoils and the quenching fixture. Since the bars are heated to hightemperatures as described, it is desirable to prevent undue heating ofthe parts of this conveyor mechanism which come into contact with them,and accordingly provision is made for cooling the conveyor. As shown inFig. 9, each of the spindles 71 is provided with a central bore 99 whichextends from its outer end to approximately the mid-plane of the smallfriction wheel 76, and a tube 100 of smaller outer diameter than bore 99is inserted therein to a position near the inner end thereof. The otherend of each of these tubes is connected with the oil supply pipe 65through a pet cock 101, and thus oil from the same source as thequenching oil for fixture 34 is supplied under pressure to the inner endof each bore 99, whence it flows to the outer end and discharges asindicated by the arrows 102 into a trough 103 connected with reservoir67, from which it is withdrawn by pump 66 at 104 and returned to thesystem through the cooling chamber 68.

Pressure rolls are provided above certain of the conveyor rollers formaintaining the bars 30 in proper vertical alignment as they travelthrough the machine and also for assuring frictional contact between thelower edges of the bars and the friction wheels 76. Referring to Fig.10, each pressure roll is grooved to receive the upper edge of the bars30 and is rotatably mounted on one end of a crank arm 111 having itsopposite end journaled in a bearing block 112 mounted on channel 50. Acoil spring 115 is mounted between a lug 116 on the block 112 and a lug117 on the crank 111 in position to bias the arm in clockwise directionas viewed in Fig. 8, and a bolt 118 carried by arm 111 serves as anadjustable stop limiting downward movement of the pressure rolls.

In operation as the successive bars travel through the machine, theypass under the rolls 110 and cause the latter to rise against thesprings 115, the springs thus serving to exert downward pressure on thebars to maintain them in driven contact with the friction wheels 76.Furthermore, with the rolls 110 grooved as shown, the bars are held inproper lateral and vertical relation with the coil fixtures 33 and 34 toassure that only the desired portion of each bar passes through thesefixtures as described. It should in this connection be noted that eachof the rolls 110 in Fig. 8 is provided with the biased crank mountingdescribed, the showing of this mechanism being eliminated for most ofrolls 110 in Figs. 7 and 8 for simplicity of illustration.

This machine is accordingly well suited for performing the heat treatingmethod described in connection with Fig, 2, and it has been successfullyoperated to produce Jordan bars having the properties of differentialhardness illustrated by Fig. 6. The machine is readily adjustable asdesired in accordance with the temperatures at the heating fixtures, thetemperature and pressure of the quenching oil and the rate of travel ofthe bars required to produce a predetermined condition of differentialhardness in the finished bars, and thus it provides for accuraterepetition of the same conditions for each of a plurality of successivebars to assure uniform properties in all the bars of a set.

This application is a division of our application Serial No. 145,838,filed February 23, 1950, now Patent No. 2,686,460, issued August 17,1954.

While the article and method herein described, and the form of apparatusfor carrying this method into effect, constitute preferred embodimentsof the invention, it is to be understood that the invention is notlimited to this precise article, method and form of apparatus, and thatchanges may be made in either without departing from the scope of theinvention which is defined in the appended claims.

What is claimed is:

l. The method of differentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of applying heat to said bar throughout the thickness thereofalong a limited portion of the width of said bar adjacent said workingedge to heat said working edge portion to a predetermined relativelyhigh temperature range. quenching said bar to cause hardening of saidworking edge portion, thereafter applying heat to said bar throughanother limited portion of the width thereof including said supportingedge, and controlling said last named heating step to limit the maximumtemperature in said bar during said step to a temperature rangesubstantially lower than said high temperature range to draw the temperalong said supporting edge portion and to provide said increasedtoughness therein.

2. The method of differentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the Working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of applying heat to said bar throughout the thickness thereofalong a limited portion of the width of said bar adjacent said workingedge to heat said working edge portion to a predetermined relativelyhigh temperature range, quenching said bar to cause hardening of saidworking edge portion, thereafter applying heat to said bar throughanother limited portion of the width thereof including said supportingedge while excluding said working edge portion from the directapplication of heat, controlling said last named heating step to limitthe maximum temperature in said bar during said step to a temperaturerange substantially lower than said high temperature range to draw thetemper along said supporting edge portion and to provide said increasedtoughness therein, and air cooling said bar to effect reheating of saidworking edge portion thereof by conduction from said supporting edgeportion and resulting reduction in the degree of hardness of saidworking portion from the degree of hardness imparted thereto by saidfirst named heating step and quenching step.

3. The method of differentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of applying heat to said bar throughout the thickness thereofalong a limited portion of the width of said bar adjacent said workingedge to heat said working edge portion to a predetermined relativelyhigh temperature range, quenching said bar to cause hardening of saidworking edge portion, thereafter applying heat to said bar throughanother limited portion of the width thereof including said supportingedge, and controlling said last named heating step to limit the maximumtemperature in said bar during said step to a temperature rangesubstantially lower than said high temperature range to draw the temperalong said supporting edge portion and to provide said increasedtoughness therein, and thereafter machining said supporting edge portionto provide attaching means for said bar.

4. The method of differentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of applying heat to said bar throughout the thickness thereofalong a limited portion of the width of said bar adjacent said workingedge to heat said working edge portion to a predetermined relativelyhigh temperature range, substantially immediately quenching said bar tocause hardening of said working edge portion without materiallyaffecting the hardness of the remainder of said bar, then applying heatto said bar through another limited portion of the width thereofincluding said supporting edge while excluding said working edge portionfrom the direct application of heat but before cooling of said workingedge portion to room temperature, controlling said last named heatingstep to limit the maximum temperature in said bar during said step to atemperature range substantially lower than said high temperature rangeto draw the temper along said supporting edge portion and to providesaid increased toughness therein, and air cooling said bar to effectreheating of said working edge portion thereof by conduction from saidsupporting edge portion and resulting reduction in the degree ofhardness of said working portion from the degree of hardness impartedthereto by said first named heating step and quenching step.

5. The method of differentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of passing a limited portion of the width of said bar adjacentsaid working edge through a first high frequency induction field ofpredetermined high intensity to heat said working edge portion to apredetermined relatively high temperature range, quenching said bar tocause hardening of said working edge portion, thereafter passing anotherlimited portion of the width of said bar including said supporting edgethrough a second high frequency induction field of predetermined lowerintensity to heat said supporting edge portion to a temperature rangelower than said high temperature range and thus to draw the tempertherefrom and provide said increased toughness therein, and air coolingsaid bar to effect re heating of said working edge portion thereof byconduction from said supporting edge portion and resulting reduction inthe degree of hardness of said working portion from the degree ofhardness imparted thereto by said first named heating step and quenchingstep.

6. The method of dilferentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of continuously advancing successive said bars lengthwise thereofthrough first and second heating stations, applying heat at said firstheating station to a limited portion of the width of each successivesaid bar adjacent the working edge thereof to heat said working edge toa predetermined relatively high temperature range, quenching each saidsuccessive bar intermediate said heating stations to cause hardeningthereof along said working edge, applying heat at said second heatingstation to a limited leading portion of each said successive bar alongsaid supporting edge thereof simultaneously with the application of heatat said first heating station to a trailing portion of said bar adjacentsaid working edge thereof, and controlling the heat applied to said barsat said second heating station to a substantially lower temperaturerange than said high temperature range to draw the temper along saidsupporting edge portion and to provide said increased toughness therein.

7. Apparatus for heat treating a plurality of successive integrallyformed and initially homogeneous elongated cutter bars of the characterdescribed having a width greatly in excess of the thickness thereof toprovide increased hardness along the working edge of said bars andincreased toughness along the opposite or supporting edge, comprising aframe, means on said frame for continuously conveying successive saidbars lengthwise thereof along said frame, heating means forming a firstheat ing station for applying heat to said bars, means supporting saidheating means on said frame in position to apply heat only to a limitedportion of the width of each successive said bar adjacent the workingedge thereof, means for controlling the heat applied to each said bar atsaid first heating station to heat said working edge to a predeterminedrelatively high temperature range, means on said frame adjacent saidfirst heating station for quenching each said bar to cause hardeningthereof of said bar along said working edge, additional heating meansforming a second heating station, means supporting said additionalheating means on said frame in pqsi:

tion to apply heat to each successive said bar only in a limited portionthereof adjacent the supporting edge thereof following passage of saidbar beyond said quenching means, and means for controlling the heatapplied to said bar at said second heating station to limit the maximumtemperature in said bar at said second heating station to a temperaturerange substantially lower than said high temperature range to draw thetemper along said supporting edge and to provide said increasedtoughness therein.

8. Apparatus for heat treating a plurality of successive integrallyformed and initially homogeneous clongated cutter bars of the characterdescribed having a width greatly in excess of the thickness thereof toprovide increased hardness along the working edge of said bars andincreased toughness along the opposite or supporting edge, comprising aframe, means on said frame for continuously conveying successive saidbars lengthwise thereof along said frame, heating means on said framefor applying heat to each said bar throughout the thickness thereofalong a limited portion of the width of said bar adjacent said workingedge to heat said working edge portion to a predetermined relativelyhigh temperature range, means adjacent said heating means for quenchingeach said bar to cause hardening of said working edge portion, andadditional heating means on said frame spaced from said quenching meansfor applying heat only through another limited portion of the width ofeach said bar adjacent said supporting edge thereof following quenchingof said bar to heat the portion of said bar adjacent said supportingedge to a predetermined temperature range substantially lower than saidhigh temperature range and thus to draw the temper along said supportingedge portion and to provide said increased toughness therein.

9. Apparatus for heat treating a plurality of successive integrallyformed and initially homogeneous elongated cutter bars of the characterdescribed having a width greatly in excess of the thickness thereof toprovide increased hardness along the working edge of said bars andincreased toughness along the opposite or supporting edge. comprising aframe, means on said frame for continuously conveying successive saidbars lengthwise thereof along said frame, means including a firstfixture for creating a first high frequency induction field ofpredetermined high intensity, means supporting said fixture on saidframe in position to receive through said field a limited portion of thewidth of each successive said bar adjacent the working edge thereof toheat said Working edge portion to a predetermined relatively hightemperaturc range. means on said frame adjacent said first fixture forquenching each said bar to cause hardening of said working edge portion,means including a second fixture for creating a second high frequencyinduction field of predetermined lower intensity than said first field,and means supporting said second fixture on said frame in spacedrelation with said first fixture and said quenching means in position toreceive through said second field another limited portion of the widthof each said bar including the supporting edge thereof to heat saidsupporting edge portion to a temperature range substantially lower thansaid high temperature range and thus to draw the temper along saidsupporting edge and to provide said increased toughness therein.

l0. Apparatus for heat treating a plurality of successive integrallyformed and initially homogeneous elongated cutter bars of the characterdescribed having a width greatly in excess of the thickness thereof toprovide increased hardness along the working edge of said bars andincreased toughness along the opposite or supporting edge. comprising aframe, means on said frame for continuously conveying successive saidbars lengthwise thereof along said frame, heating means on said framefor applying heat to each said bar throughout the thickness thereofalong a limited portion of the width of said bar adjacent said workingedge to heat said working edge portion to a predetermined relativelyhigh temperature range, a supply source of quenching fiuid on saidframe, means adjacent said heating means for directing quenching fluidfrom said supply source upon each said bar to cause hardening of saidworking edge portion thereof, additional heating means on said framespaced from said quenching means for applying heat along another limitedportion of the width of each said bar including said supporting edgethereof following quenching of said bar to heat the portion of said baradjacent said supporting edge to a predetermined temperature rangesubstantially lower than said high temperature range and thus to drawthe temper along said supporting edge portion and to provide saidincreased toughness therein, and means for circulating quenching fluidfrom said supply source in heat exchanging rclation with said conveyingmeans to prevent overheating thereof.

ll. Apparatus for heat treating a plurality of successive integrallyformed and initially homogeneous elongated cutter bars of the characterdescribed having a width greatly in excess of the thickness thereof toprovide increased hardness along the working edge of said bars andincreased toughness along the opposite or supporting edge, comprising aframe, a plurality of conveyor units arranged in spaced relation on saidframe and each including rotatable means for supporting one edge of oneof said bars, means for maintaining said bars in frictional contact withsaid rotatable means, means for driving said rotatable means to causelengthwise travel of said successive bars along said frame, meansincluding a first fixture on said frame for applying a first highfrequency induction field of predetermined high intensity to a limitedportion of the width of each said bar adjacent the working edge thereofto heat said working edge portion to a predetermined relatively hightemperature range, means on said frame adjacent said first fixture forquenching each said bar to cause hardening of said working edge portion,means including a second fixture on said frame in spaced relation withsaid quenching means for applying a second high frequency inductionfield of predetermined lower intensity than said first field to anotherlimited portion of the width of each said bar including said supportingedge thereof to heat said portion to a temperature range substantiallylower than said high temperature range and thus to draw the temper alongsaid supporting edge and to provide said increased toughness therein,and means for adjusting the speed of said driving means in accordancewith the intensities of said fields to control said temperature range.

12. The method of differentially hardening an integrally formed andinitially homogeneous elongated cuttcr bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of applying heat at a first heating station to said bar throughworking zone thereof adjacent said working edge and of substantialcross-section less than one-half the width of said bar while limitingsaid application of heat to a relatively small portion of the length ofsaid bar, controlling said heating step to heat said zone to apredetermined relatively high temperature range, continuously movingsaid bar with respect to said heating station to cause said applicationof heat progressively to said zone along the entire length of said bar,continuously quenching said heated zone of said bar at a quenchingstation closely adjacent said heating station to cause hardening of saidzone, thereafter applying heat at a second heating station to said baralong another zone thereof including said supporting edge and extendingacross less than the full width of said her to exclude said working zonethereof while limiting said application of heat at said second heatingstation to a relatively small portion of the length of said bar,controlling said last named heating step to limit the maximumtemperature in said bar during said step to a range substantially lowerthan said high temperature range to draw the temper along saidsupporting edge portion and to provide said increased toughness therein,and continuously moving said bar with respect to said second heatingstation to cause said application of heat progressively to said baralong the entire length thereof.

13. The method of differentially hardening an integrally formed andinitially homogeneous elongated cutter bar of the character describedhaving a width greatly in excess of the thickness thereof to provideincreased hardness along the working edge thereof and increasedtoughness along the opposite or supporting edge which comprises thesteps of applying heat at a first heating station to said bar through alimited working zone thereof adjacent said working edge and ofsubstantial cross-section less than one-half the width of siad bar whilelimiting said application of heat to a relatively small portion of thelength of said bar, controlling said heating step to heat said zone to apredetermined relatively high temperature range, continuously movingsaid bar with respect to said heating station to cause said applicationof heat progressively to said zone along the entire length of said bar,continuously quenching said heated zone of said bar at a quenchingstation closely adjacent said heating station to cause hardening of saidworking zone, thereafter applying 'heat at a second heatlog station tosaid bar through another limited zone thereof including said supportingedge and extending across less than the full width of said bar toexclude said working zone thereof while limiting said application ofheat at said second heating station to a relatively small portion of thelength of said bar, controlling said last named heating step to limitthe maximum temperature in said bar during said step to a rangesubstantially lower than said high temperature range to draw the temperalong said supporting edge portion to provide said increased toughnesstherein, continuously moving said bar with respect to said secondheating station to cause said appiication of heat progressively to saidbar along the entire length thereof, and air cooling said bar to effectreheating of said working zone thereof and resulting reduction in thedegree of hardness of said working zone from the degree of hardnessimparted thereto by said first heating step and said quenching step.

References Cited in the file of this patent UNITED STATES PATENTS2,358,834 Sonics Sept. 26, 1944 2,371,459 Mittelmann Mar. 13, 19452,424,794 Brown July 29, 1947 2,598,694 Herbenar June 3, 1952 2,604,419Herbenar July 22, 1952 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION atent No. 2,831,788 Adam E. Bridge et a1. April 22, 1958 Itis hereby certified that error appears in the printed specification of;he above numbered patent requiring correction and that the said LettersPatent :hould read as corrected below.

line 34, for "to the direction" read to the portion read Bar thiclmessBar thickness do k line 1'7, for "siad" read said Column 2, :olumn 5,line 23, for Lnch column 13,

Signed and sealed this 24th day of June l958.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Cunnissioner of Patents AttestingOfficer

1. THE METHOD OF DIFFERENTIALLY HARDENING AN INTEGRALLY FORMED AND INITIALLY HOMOGENEOUS ELONGATED CUTTER BAR OF THE CHARACTER DESCRIBED HAVING A WIDTH GREATLY IN EXCESS OF THE THICKNESS THEREOF TO PROVIDE INCREASED HARDNESS ALONG THE WORKING EDGE THEREOF AND INCREASED TOUGHNESS ALONG THE OPPOSITE OR SUPPORTING EDGE WHICH COMPRISES THE STEPS OF APPLYING HEAT TO SAID BAR THROUGHOUT THE THICKNESS THEREOF ALONG A LIMITED PORTION OF THE WIDTH OF SAID BAR ADJACENT SAID WORKING EDGE TO HEAT SAID WORKING EDGE PORTION TO A PREDETERMINED RELATIVELY HIGH TEMPERATURE RANGE, QUENCHING SAID BAR TO CAUSE HARDENING OF SAID WORKING EDGE PORTION, THEREAFTER APPLYING HEAT TO 